This proposal is on genetic rearrangements induced by the bacterial transposable elements. These include the drug resistance transposons and the insertion sequences associated with conjugal plasmids, such as the resistance factors and the E. coli sex factor F. Many different transposable elements are known; Tn5, Tn10 and IS3 are considered here. These elements all undergo transposition, a process by which a gene or a sequence of DNA at one genetic locus can reappear at new sites either on the same chromosome or on others. Once inserted into a new chromosomal location, the transposable elements can be spontaneously deleted and the original chromosomal sequences restored by a process called precise excision. The primary goal of this proposal is to determine the molecular mechanisms of transposition and precise excision, including the relationship of the precise excision mechanism to transposition and other biological processes. Techniques of microbial genetics are used and mutants of E. coli that affect precise excision and transposition are studied. We propose to characterize mutants that affect precise excision and transposition, to isolate new classes of mutants affecting transposition and to characterize a gene on the sex factor F, whose product stimulates both precise excision of Tn5 and Tn10 and recombination through IS3.